Compressor control



y 9, 1963 D. T. KOCH ET AL 3,096,926

COMPRESSOR CONTROL Filed March 19, 1962 5 Sheets-Sheet 1 MM, 22 55 33 6Ak L ANA kk T A KK K.K. K.K. PP P mm mm PP 2 l2 l2 I2 I2 cc c co cc ccLL LL LL LL L| YY YY Y cc cc um mm c N m mHN TCA S fl a W m 1T.R. m mm mAU L y 9, 1963 D. T. KOCH ET AL 3,096,926

COMPRESSOR CONTROL Filed March 19, 1962 5 Sheets-Sheet 2 INVENTOR.DONALD T. KocH WILLIAM R. BOHANNAN FE? gfi BY 2 22 ATTORNEYS y 9, 1963D. T. KOCH ET AL 3,095,926

COMPRESSOR CONTROL Filed March 19, 1962 3 Sheets-Sheet 3 mag.

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INVENTOR.

DONALD T. Kocn WILLIAM R. BOHANNAN QULQL A'TTO RNEYS United StatesPatent 3,096,926 CfiMPRESSOR CONTRGL Donald T. Koch, Birmingham, Mich,and William R.

Bohannan, Caracas, Venezuela, assignors to The Cooper-BessemerCorporation, Mount Vernon, Ohio,

a corporation of Ohio Fiied Mar. 1%, 1962, Ser. No. 180,767 4 Claims.(Cl. 230-4) This invention relates to a control for reciprocatingcompressors and is particularly directed to a control that is intendedfor use with relatively large, engine driven compressors in servicewherein the suction and discharge pressures are both subject tosubstantial variation. Such compressors are commonly used on gastransmission pipelines and in gas storage service.

It is desirable that the engine driving a reciprocating gas compressorbe held very close to its point of optimum loading and performance, andthat it be not overloaded. Commercial considerations suggest that theengine load be held within +3 percent and percent of constant loading.Control within this narrow range is very difficult to accomplishmanually, and present automatic systems with which we are familiar areunsuitable and unreliable. Most automatic systems are sensitive only todischarge pressure and to engine speed and torque so that they controlthe engine load after the overload has occurred, and do not anticipateit. The present invention provides means to control the compressionratio of a reciprocating compressor in accordance with variations ofboth suction pressure and discharge pressure. By this expedient, aconventional form of engine governor may be used to control engine speedand it will be found that the horsepower output of the engine remainsconstant within the above described commercial limitations.

The primary object of the present invention, therefore, is to providemeans to control the compression ratio of a reciprocating compressor inaccordance with variations in both the suction and discharge pressureswith which the machine is operating.

Other objects and advantages of the invention will become apparent fromthe following detailed description of a preferred embodiment thereof,reference being had to the accompanying drawings, in which:

FIG.1 is a diagrammatic view of a compressor and a control thereforembodying the present invention;

FIG. 2 is a plan view, with parts in section and parts broken away of acontrol embodying the present invention;

FIG. 3 is a section on line 3-3 of FIG. 2;

FIG. 4 is a diagrammatic view of a modified form of the invention; and

FIG. 5 is a diagrammatic plan View of a modified form of sensing plate.

The drawings show the present invention in conjunction with an enginewhich may be, for example, a gas fueled engine having angle compressorcylinders 12 and 13. This engine-compressor configuration isconventional and widely used. If the compressor is used for gastransmission service, it will take gas from a suction line 14 at arelatively high pressure, for example, 600 psi. and will discharge itinto a discharge line 16 at a higher pressure, for example, 850 psi. Aconventional compressor of this type is provided with regulating devicesin the form of clearance pockets at each end of the compressor cylinder(the cylinder being double-acting) and with unloading valves by whicheither end of a cylinder may be opened to the suction line during boththe suction and compression strokes so that no energy is expended in thecylinder. Opening of a clearance pocket changes the compression ratio ofthe afliected end of the cylinder and therefore pumps a greater volumeof gas at a lower pressure rise, while opening of an unloading valve, ofcourse, effectively puts the load on the affected end of a cylinder atzero.

No specific disclosure of the construction of the valves forstep-unloading of the compressor need be made herein, since these valvesare conventional. The step-unloading devices are designated A1 to A-6inclusive and are duplicated in each compressor cylinder. It will bereadily apparent that a greater or lesser number of step-unloadingdevices may be used without departing from the teachings of the presentinvention.

In the operation of engine driven compressors it is always desirable totake full advantage of the full rated horsepower of the engine wheneverpossible. At the same time it is highly undesirable to overload theengine even for a short time in the event of a change of the pressureconditions. Normally, the only way an engine can be operated at optimumefficiency when both the suction and discharge pressures vary is toattempt to follow the horsepower curve of the engine as reflected inthese pressures. Such a curve has heretofore required the operator tomake manual changes in the percent clearance in the compressor cylindersby opening or closing the clearance pockets and unloading valves. Thepresent invention analyzes the prevailing pressure conditions, and doesautomatically what has heretofore been accomplished very inetfectivelyby manual operation so that the present invention is capable ofoperating with much greater pre cision.

The present invention includes means responsive to a variation of bothsuction and discharge pressures, and may comprise a movable contactmember 20 carried in a suitable holder and biased outwardly intoelectrical contact with a plate by a spring 21. A cylinder 22 isconnected to the compressor discharge line 16 by a pipe 24. A piston 26in the cylinder 22 is connected to a yoke 28 having a slot 30 therein,in which the stem of the contact member 20 is received. Movement of thepiston 26 will, therefore, cause a movement of the contact member 20 inone direction. Since cylinder 22 contains gas at discharge pressure theposition of the contact member will be determined by and responsive tochanges in this pressure.

Disposed at right angles to the discharge pressure cylinder 22 is asecond cylinder 32 connected by a pipe 34 to the suction line 14 of thecompressor, and having a piston 36 therein connected to a second yoke38. Yoke 38 has a slot 40 in which the stem of the contact member 24? isalso received. As the suction pressure increases or decreases theleft-to-right position of the contact member 24 will be adjusted by theyoke 38, and if the dis charge pressure is constant the stem of thecontact member 20' will merely slide in the slot 30 of the dischargepressure yoke. Similarly, as the discharge pressure is changed, thestern of the contact member 20 will slide in the slot 40 of the suctionpressure yoke 38. Thus, be-

. 3 cause the contact member is received in the perpendicularly disposedslots 30 and 40 of the yokes 28 and 38 its position will depend on themagnitude, at any time, of both the suction and discharge pressures, andthe position reflects the algebraic sum of the pressures.

The contact member 20 is moved over a stationary contact plate 44, andthe point of the member 20 is in electrically conductive contact withthe surface of the plate. The contact plate 44 is divided into aplurality of seg ments 45, 46, 47, 48 and 4,9 shaped in accordance withthe horepower output requirement of the engine ltl for given ranges ofvariation of suction and discharge pressures, as will become apparent.The subdivision of the contact plate 44 can be carried :to any desireddegree to give greater or less precision to the operation of the engine.

When the suction and discharge pressures bear a predeterminedrelationship to each other, all of the step-unloading .devices can beclosed and the full horsepower ,output of the engine utilized in thecompressor. In the event that the discharge pressure should increasebeyond a predetermined value while the suction pressure remains thesame, it would become desirable, to prevent overloading, .to open one ormore of the step-unloading devices, probably in the form of one or moreclearance pockets. This increase in discharge pressure, however, mightbe accompanied by a decrease in suction pressure. In this event no.change in the effective volume of the compressor cylinder needbe .madeunless the relationship of the pressures causes a substantial loadchange on the engine. From the configuration of the division linesbetween the segments of contact plate 44 it will be noted that, at lowsuction pressures, the discharge pressure may vary substantially withoutchanging the load on the engine or prime mover. At high suctionpressures, however, a small variation in discharge pressure requires achange in the compression ratio by the operation of one or morestep-unloading devices. As the suction pressure increases a reduction inthe compression ratio would occur if the discharge pressure were to heheld constant, and the flow of gas through the compressor would bereduced, and the horsepower output of the engine would fall off. Byopening one or more clearance pockets the flow can be raised which, inturn, raises the horsepower requirement of the prime mover since it isrequired to pump more gas through the line.

A suitable mechanism :for opening and closing the stepunloading devicesin response to a movement of the contact 20 over the segmented plate 44is shown diagrammatica'lly in FIG. 1. As shown, the step-unloadingdevices are fluid operated and the flow of fluid thereto is controlledby an appropriate series of solenoid operated valves. The disclosure ofthe valves is in accordance with the conventions of the AmericanStandards Association.

in the energized position permits fluid to flow through it (this "issymbolized by the upper square having the horizontal arrow). In thede-energized position the spool or other movable valve element stands insuch a position that the flow of fluid is cut oil, as symbolized by theslanting arrow'in the lower square. A dotted line 51 connects the valve50a with a diagrammatically shown solenoid 52a indicating which of theseveral solenoids operates the respective valves.

The fluid control valves similar in form and operation to valve 50a aregiven the reference numerals 50b, 50c, 50d and 50a in FIG. 1. Similarly,solenoids for operating the respective valves are indicated at 52a, 52b,52c, 52d and 52e. The operating contact segments of the contact plateare given the reference characters a, b, c, d and e, and these areconnected electrically to relays 53a, 53b, 53c, 53d and 53e. The relayscarry the additional designations TDa, TDb, TDc, TDd and TDe. The TDdesignation indicates that the relay has a time delay opera- .tion, :andin this instance the delay occurs upon opening. The relays arefast-closing, slow-opening devices.

' Except for relay 53a which has a single contact pair, each of therelays 53b, 53c, 53d and 53a is provided with two sets of operatingcontacts, one in each series with its respective solenoid and the otherin parallel with the coil of its preceding relay to act as holdingcontacts. Thus, relay 53b has a set of contacts 54b in series withsolenoid 52b to close the circuit through the solenoid and has anadditional set of contacts 55b in parallel with the coil of relay 53awhich, when closed, will maintain the relay 53a closed even though itscircuit from contact segment a should be opened.

The effect of the delayed opening relay system shown is to make theoperation of the step-unloading devices cumulative. Thus, if a set ofclearance pockets is opened by valve Stla, operation of valve b opens anadditional set of clearance pockets while those previously opened byvalve 50a remain open.

The electrical circuit for the operation of relays 53a to 53c inclusivemay comprise a simple D.C. circuit, one side of which is connected toground (or negative) while the positive side is connected to the movablecontact member 20. When contact member 20 is electrically in contactwith operating segment a, for example, the circuit to ground iscompleted through relay 53a, and when contact 20 moves to segment b thecircuit to relay 53b is completed, relay 53a being held closed bycontacts b as explained above.

As indicated in FIG. 1 of the drawing each of the compressor cylindersC1 and C-2 is provided with clearance pockets A-l, A-2 and A-3 at thehead end, clearance pockets A-4 and A-6 at the rod end and an unloadervalve A-S at the suction manifold. Clearance pockets A-1 and A-4 in eachcylinder are opened by fluid pressure supplied from a header throughvalve 50a when the latter is open. Valve 50b, when opened, will passoperating fluid from the header to clearance pockets A2; valve 500 whenopened will pass operating fluid to clearance pockets A-S; valve 5001when opened will pass operating fluid to clearance pockets A3; and theunloading valves A'5 in each cylinder are opened when operating fluid ispassed from the header 60 through valve 50c.

If desired, a conventional speed governor 62 may be used to controlengine speed and may take its operating power from the header 60 and itssensing function from a line 64 connected to the discharge manifold -16.

In operation, assuming that the compressor is running at normal suctionand discharge pressures, these pressures will be reflected respectivelyin cylinders 32 and 22 and the yokes 38 and 28 will cause the movablecontact member 20 to stand over that portion of contact plate 44 aboveand to the left of segment a as these segments are shown in FIGS. 1 and3. The engine will be running under normal governor control with all ofthe compressor step-unloading devices closed.

A If the discharge pressure of the compressor increases so that the loadon the engine increases (suction pressure remaining constant) theincrease in pressure in cylinder 22 will move yoke 28 downwardly inFIGS. 1 and 2 and if the magnitude of the increase is sufficient,movable contact 20 will enter segment a of the contact plate 44. Thecircuit to relay 53a will be completed, contacts 54a will be closed,solenoid 52a will be energized, and valve 50a will shift to itsenergized position. Control fluid can now flow from header 60 toclearance pockets A1 and A-4 in each compressor cylinder. The engine isnow running at full load with a lower compression ratio, and thehorsepower output of the engine remains unchanged Should the dischargepressure continue to rise, the increased pressure in cylinder 22 willmove the contact member 20 from segment a to segment b of the plate 44.The circuit to relay 53b will be completed, contacts 54b will be closedto energize solenoid 52b and at the same time contacts 55b will close toestablish a holding circuit for the relay 53a. As previously noted, therelays 53a to 53c are of the delayed opening type so that there is timefor the holding circuit to be established before the previously closedrelay can open. Since the circuits to solenoids 52a and 53b are now bothclosed, valves 50a and 50b will both be energized and clearance pockets1, 2 and 4 will be opened, further reducing the compression ratio of thecompressor.

If the discharge pressure continues to increase, the movable contactmember 20 will successively enter segments 0, d and e to maintain thehorsepower output of the engine substantially constant.

Assuming now that the discharge pressure were to remain constant, andthe suction pressure were to increase, the movable contact member 20will be moved first by the yoke 38 into segments a, b and c with thesame effect as described above.

In the event that both suction and discharge pressures vary, which isthe more usual case, the position of the movable contact member 20 willbe established by the combined effect of both pressures, through themovement imparted thereto by both yokes 28 and 38, and its position isthe algebraic sum of the movements caused by the two pressures.

The operation of the parts upon a decrease in pressure is, of course,the reverse of that described above. As the movable contact 20 movesfrom segment d to the lower segment 0, for example, relay 53d opensafter a predetermined time interval, solenoid 52d is de-energized andvalve SM is closed, closing clearance pockets 43.

The drawings show a control which depends for its operation on anelectrical contact between a moving stylus and a segmented contactplate. It is, however, Within the purview of the invention to provide acontrol which does not depend on an electrical contact, but whichoperates electronically by a change in output of a circuit including amoving pick-up and a segmented stationary control element. For example,a photoelectric scanning device comprising a light source 100 and amovable photoelectric cell 101 having its output varied by varying theoptical density of a segmented stationary control plate 102 can bereadily substituted. Such an electrical output from the photocell 101can be used to trigger consecutive zener diodes 163a, 103b, 1630, 103dand 103e biased by resistors 104a, 1041:, 104e, 194a and 104e todifferent levels of operation for consecutive operation. In this system,a strong light 100 placed behind the segmented stationary control plate1il2 would be used, the plate being progressively shaded in opticaldensity from segment to segment. As the photocell is moved over thepattern by the variation in suction and discharge pressures, it passesfrom area A to area B to area C, etc, which are shaded respectivelydarker. The result of this scanning operation is a variation in thephotocell output from one area to another. This variation can easily besensed by diodes 103a, 103b, 103e, 103d and 1032 and translated intovoltage outputs corresponding to the particular scanned areas. Thesevoltage outputs can then be fed directly or in an amplified condition tothe circuits comprising relays 53a, 53b, etc. Similarly, separatep'hotocells may be placed behind each of the segmented stationary plateareas and a single light source moved by the yokes 28 and 38 to feed therelay system. In such a system the segmented plate would have a uniformoptical density.

It is also intended that the appended claims shall include pneumatic orhydraulic means for sensing the movement of the stylus or movablecontrol element from one segment to another of the stationary controlelement, in which case the segments may be physically spaced from eachother at different elevations.

While reference has been made throughout the specification to an enginedriven compressor, the term engine is intended to embrace other knownprime movers such as a gas or steam turbine. Thus, while the inventionhas been described in conjunction with a specific form and dispositionof the parts, it should be understood that the disclosure is highlydiagrammatic and is simplified for purposes of understanding theprinciples of the invention and of one form thereof. It will be apparentto those skilled in the art that numerous modifications and changes maybe made therein without departing from the scope of the appended claims.

What we claim is:

1. In a control system for a compressor having means to change thecompression ratio of the compressor While running, the combination of(1) a single movable control element,

(a) moved in one direction by a change in compressor discharge pressureand (b) moved in a direction at right angles to said first movement by achange in compressor suction pressure,

(2) a stationary control element operatively associated with saidmovable control element,

(a) having its surface segmented .into areas representing l3. summationof suction and discharge pressures at which the compressor operates atsubstantially constant horsepower,

(3) means to sense the presence of said movable concontrol element overany of the segments of said stationary control element, and

(4) means responsive to said sensing means to change the compressionratio of the compressor to maintain the power input to the compressorsubstantially constant.

2. In a control for a reciprocating compressor having a plurality ofindependently operable step unloading .devices in each cylinder, thecombination of (a) means responsive to compressor suction pressure;

(b) means responsive to compressor discharge pressure;

(c) a stationary contact plate having (1) a plurality of segmentsinsulated from each other (a) each of said segments representing asummation of suction and discharge pressures at which the compressoroperates at substantially constant horsepower;

(d) a movable contact member in electrical contact with said stationarycontact plate;

(e) means to move said movable contact member along a first axis by saidmeans responsive to suetion pressure;

(7) means to move said movable contact member along an axisperpendicular to said first axis by said means responsive to dischargepressure;

(g) a plurality of valve means to control the flow of operating fluid tosaid step-unloading devices (1) and corresponding in number to thenumber of segments in said stationary contact plate;

(h) and means initiated by engagement of said movable contact with eachof said insulated segments to operate a respective one of said valveswhereby said valves are operated sequentially as the algebraic sum ofsuction and discharge pressures increases and said step-unloadingdevices are operated sequentially to maintain the power requirement ofsaid compressor substantially constant.

3. The combination of means defined in claim 2 and holding means to[retain in an open position a previously opened valve as the algebraicsum of pressures increases.

4. In a control system for a compressor having means to change thecompression ratio of the compressor While running, the combination of(1) a single movable element (a) moved in one direction by a change incompressor discharge pressure and ([2) moved in a direction at rightangles to said firstmovement by a change in compressor suction pressure'(2) a stationary control element operativeiy associated with saidmovable control element,

(a) having its surface segmented into areas of substantially constantcompressor power input, (3) means 'to sense the presence of said movablecontrol element over any of the segments of said stationary controlelement, and (4) means responsive to said sensing means to change thecompression ratio of the compressor to main- References Cited in the'file of this patent UNITED STATES PATENTS Wallene Apr. '9, 1935Paul'lin July 25, 1939 Miller Nov. 14, 1939 G'arbaccio July 8, 1952Corson et a l. May 2, 196-1 Emmel Mar. 13, 1962

1. IN A CONTROL SYSTEM FOR A COMPRESSOR HAVING MEANS TO CHANGE THECOMPRESSION RATIO OF THE COMPRESSOR WHILE RUNNING, THE COMBINATION OF(1) A SINGLE MOVABLE CONTROL ELEMENT, (A) MOVED IN ONE DIRECTION BY ACHANGE IN COMPRESSOR DISCHARGE PRESSURE AND (B) MOVED IN A DIRECTION ATRIGHT ANGLES TO SAID FIRST MOVEMENT BY A CHANGE IN COMPRESSOR SUCTIONPRESSURE, (2) A STATIONARY CONTROL ELEMENT OPERATIVELY ASSOCIATED WITHSAID MOVABLE CONTROL ELEMENT, (A) HAVING ITS SURFACE SEGMENTED INTOAREAS REPRESENTING A SUMMATION OF SUCTION AND DISCHARGE PRESSURES ATWHICH THE COMPRESSOR OPERATES AT SUBSTANTIALLY CONSTANT HORSEPOWER, (3)MEANS TO SENSE THE PRESENCE OF SAID MOVABLE CONCONTROL ELEMENT OVER ANYOF THE SEGMENTS OF SAID STATIONARY CONTROL ELEMENT, AND (4) MEANSRESPONSIVE TO SAID SENSING MEANS TO CHANGE THE COMPRESSION RATIO OF THECOMPRESSOR TO MAINTAIN THE POWER INPUT TO THE COMPRESSOR SUBSTANTIALLYCONSTANT.